Who says LiPo batteries are dangerous?

Had a bit of fun with some LiPo batteries today. I had an opportunity to purposely burn up some LiPo cells today to see if a simply aluminum enclosure can contain the heat generated when they let loose.

Pretty box before the LiPo destruction

I had 4 Turnigy nano-tech 4400mah 7S Batteries in the box, connected to create a single 8800mah 14S pack. Starting with the cells fully charged, I pushed 4 amps of current into them for a little over an hour before they finally gave up. It hit 72 volts right before everything went wrong with the cells. Impressive to say the least… my money was on them failing much sooner. Temperature inside the enclosure went over 1370 degrees Celsius (the limit of my data logger) for a few seconds before settling down to 900 degrees for 5 or 6 minutes. It took about 30 minutes for it finally the cool down to 400C. The cell closest to the camera looks like it blew first and hardest… it managed to blow a penny sized hole in the aluminum at some point. That side of the enclosure was bent and cracked from the heat also.

The initial smoke is caused by the first cell letting go. The second blast which hits the camera is the other three cells from what I can see. The next test will be with 8 cells and a stronger box. 😉

So you were applying external electricity to the cells to make them explode? About 4 amp hours, right? I would be more interested in seeing the scale of destruction you could get using only the energy already stored in the fully-charged cells. The sort of destruction that might be caused by, say, a laptop battery pack on an airplane that melts/explodes/starts a fire.

Cool post though, thanks for sharing the video!

[WORDPRESS HASHCASH] The poster sent us ‘0 which is not a hashcash value.

I had the cells initially connected with 2 packs in series separate from each other, essentially giving 2 14S 4.4Ah battery packs at 58.8V. Two power supplies were connected, one to each pack. The voltage was set to drive 2A of current into each pack. I kept increasing the voltage as the test went on to make sure that current was constant. The power supplies maxed out once I reached around 66V, so I ran the two power supplies in series and connected the battery packs in parallel across the power supply (at that point, essentially a single 14S 8.8Ah pack). The current was set to 4A. The voltage kept increasing until finally I hit 72V. At that point one of the battery packs failed, causing a chain reaction of failures in the other cells.

The temperature readings inside the box are actually quite interesting. The inner aluminum wall reached well over 1300C at its peak (clipping the temperature probe) very briefly and sat at above 660C (melting temp of aluminum roughly) for almost 9 minutes. The temperature measured between two of the inner battery packs was much worse… it stayed above 660C for over 15 minutes. Luckily that didn’t result in the bottom of the box dropping out. The coolish air outside the box managed to keep everything mostly intact other than the single hole and extensive cracking.

In total, it took 103.8 minutes from turning on the power supplies until the cells failed. That’s an extra 3.5Ah of energy placed into each 4.4Ah battery….. 78% over capacity. Amazing.

Its actually quite hard to make a cell fail without abusing it like this. About the only thing that would make a cell fail while at normal charge is a puncture. Even a short across the terminals typically results in simply a rapid discharge and heating to the cell (with a bit of puffiness). If you simply wait a bit before recharging, the cell will typically recover.

Aside from a puncture or overcharging, the other common way to make a cell fail is by overdischarging it (ie- under 3V per cell) and then recharging. The resulting cloud of smoke and fire isn’t nearly as impressive as the overcharge condition though. 😉